<?php    //variable functions		$func = "sqrt";    if (is_callable($func)) { //check if  if that string contains a function name that can be called using a variable function.        echo $func(49)."<br/>";;    }		$func = "str_replace";	    $output_single = call_user_func($func, "monkeys", "giraffes", "Hundreds and thousands of monkeys\n");	    $params = array("monkeys", "giraffes", "Hundreds and thousands of monkeys\n");    $output_array = call_user_func_array($func, $params); //receives array of params	    echo $output_single."<br/>";    echo $output_array ."<br/>";?>